In an extruder-type slip-form casting machine, the concrete mix is forced by means of auger feeders through a casting mold or nozzles, whereby the casting machine is propelled by file reaction force generated by the auger feeders. The ready-cast product remains resting on the casting bed. The prestressing tendons are tensioned prior to casting and the correct location of the tendons in the concrete product being cast is secured by means of tendon guides following the progress of the casting operation. The guides support the prestressing tendons from all sides so as to keep them steady in the vertical and lateral directions against displacing forces that are invoked by the concrete mix extrusion pressure generated by the auger feeders.
In special cases, the prestressing tendons may have tied thereto transverse reinforcing steels or attachment plates placed against the wall of the casting mold. Transverse reinforcing steels may be needed, e.g., when a great number of openings must be provided in the concrete product being made. Attachment plates are employed, e.g., when the concrete product is to be attached on site to the steel frame of a building prior to the final reinforcement and post-grouting of joints, joining of concrete products to each other or the surface structures of an underlying ceiling must be adhered to the concrete products. The attachment plates may be connected to one or more prestressing tendons.
In manufacture of these special products, it is impossible to use conventional tendon guides that are designed to guide prestressing tendons in a passive fashion during the entire course of casting. Neither it is possible to secure the attachment plates to the casting bed for the travel of the casting machine thereover inasmuch as such fixed attachment plates would prevent the removal of the finished concrete product away from the casting bed. Conventional extruder-type slip-form casting machines are not suited for casting such prestressed concrete products that have their lower prestressing tendons tied to supplementary parts serving to locate prestressing tendons in predetermined position so that accessory locating equipment operating from outside the casting machine are not needed.